How can we be sure we did the right thing?

  My sister in law, also my best friend, died this past march from Meningitis at the age of 21.
  A lot of questions plague us, how, why, etc.
  I guess my main question is how can we be sure we did the right thing?  After the third day of complication after complication, the doctor sat us down and said they couldn't give her back to us.  That she was brain dead.  She was taken off life support and died.  It wasnt as instantaneous as I thought it was going to be...it looked as though her lung were trying to work...and her heart kept beating for what seemed like forever.  
  Was there really no chance for her?  Or could the doctors have been wrong?  Should we have had another medical opinion first?  I just cant help but wonder if she could still be alive or not.

Dear Erin:
I am sorry about your loss. Certainly this is a difficult thing for your
entire family.
Meningitis is a serious problem. In most cases it can be treated but sometimes
our antibiotics fail. In some cases it can result in death. According
to most definitions death typically ensues following brain death. Eventhough
the heart and lungs are wotking, if the brain dies the it becomes a matter
of time before the heart and lungs will fail as well.
Brain death is established as a diagnosis through a series of clinical
tests and has to be done in a very precise fashion according to strict
criteria. If your sister-in-law's doctors diagnosed her as brain dead after
performing the needed tests then there was unfortunately not much that could be
done for her.
I hope this helps!